For long-distance communications using optical fibers, amplifiers are used to boost signals along an optical path. Because amplifiers are one-way devices, two fibers with associated amplifiers are required for bi-directional communications using optical fibers. One common format for use with fiber optics communications is use of International Telecommunications Union (ITU) channels that define frequency spacing for multiplexed optical signals.
FIG. 1 illustrates one embodiment of bidirectional transmission of multiple optical channels using two optical fibers. Optical signals are transmitted from multiple transmitting devices 100 to multiple receiving devices 140 and from transmitting devices 150 (which can be devices 140) to receiving devices 180 (which can be devices 100).
When transmitting from devices 100, the optical signals are multiplexed by multiplexor 110 to generate a wavelength division multiplexed (WDM) or dense WDM (DWDM) optical signal. The WDM/DWDM optical signal is transmitted to amplifier 120, where the signal is strengthened and forwarded to amplifier 122. The sequence of amplification continues as necessary until the signal is received by demultiplexor 130. Amplification of transmitted optical signals is known in the art. Demultiplexor 130 demultiplexes the optical signal and distributes the signals to devices 140.
Optical signals transmitted from devices 150 to devices 180 are transmitted in a similar manner. The optical signals are multiplexed by multiplexor 190 to create a WDM or DWDM optical signal. The signal is transmitted via optical fiber to amplifiers 160 and 162 to demultiplexor 170. Demultiplexor 170 demultiplexes the WDM/DWDM optical signal and distributes the optical signals to devices 180. The bidirectional network of FIG. 1 requires two sets of multiplexors, demultiplexors, amplifiers, fibers and related interconnections and is thus inefficient network architecture.
FIG. 2 illustrates one embodiment of bidirectional transmission of multiple optical channels using circulators and interleaving filters. In the architecture of FIG. 2 a first set of optical frequencies (e.g. even ITU channels) are communicated in a first direction and a second set of optical frequencies (e.g. odd ITU channels) are communicated in the opposite direction.
A WDM or DWDM signal is transmitted to circulator 210 via optical fiber 200. Circulator 210 routes the optical signal to amplifier 220. Amplifier 220 amplifies the signal, and filter 230 filters the amplified signal. Amplifier 225 further amplifies the optical signal. The filtering and amplification are performed as necessary based on, for example, fiber length and/or signal conditions. The optical signal is eventually routed to circulator 240.
Circulator 240 routes the optical signal from amplifier 225 to optical fiber 250, which carries the optical signal to one or more receiving devices (e.g. a demultiplexor). For optical signals traveling in the opposite direction, optical fiber 250 carries signals from a transmitting device (e.g. a multiplexor) to circulator 240, which routes the optical signal from fiber 250 to amplifier 260. Amplifier 260, filter 270 and amplifier 265 amplify and filter the optical signal as necessary, and direct the optical signal to circulator 210.
Circulator 210 routes optical signals from amplifier 265 to optical fiber 200. Optical fiber 200 carries the optical signal to a receiving device (e.g. a demultiplexor). The network architecture of FIG. 2, as with the network architecture of FIG. 1, requires two sets of amplifiers. The network architecture of FIG. 2 also requires two sets of filters and at least two circulators. The network of FIG. 2 is can be more efficient than the network architecture of FIG. 1; however, the network architecture of FIG. 2 can be expensive to build and to maintain.